Methods for estimating medication adherence to antiretroviral therapy: Response to Mehta et al. (2016).

Dear Editor,

We went through with considerable interest, the article by Mehta et al. regarding adherence to antiretroviral therapy (ART) medications among people living with HIV (PLHIV) undergoing treatment in an ART clinic.[1] The research is of considerable importance since the extent of adherence to ART among PLHIV determines the quality of life and patient survival.[2] We request certain clarifications with regard to the methodology employed which would aid future researchers since the measurement of medication adherence in HIV/AIDS patients on ART is complex and no gold standard exists.[3] The authors have reported the drug adherence rate as the percentage of prescribed doses of the ART medication taken by the patient in the previous 30 days. However, the method used to query the information for estimation of the number of pills missed by the patient has not been reported by the authors. There are several methods which could have been potentially used for assessing medication adherence in the study site, which are described below.[34]

Self-reported (percentage) adherence: The patient is asked to report the number of days, in which there were episodes of missed medication during a specified period

Self-reported adherence through a validated questionnaire like Aids Clinical Trial Group: A four-item self-administered questionnaire is used for assessing patient medication adherence in the previous 7 days[5]

These self-reported adherence measures are simple to administer while permitting a rapid assessment of medication adherence. Nevertheless, they also tend to overestimate the rate of adherence[5] due to self-desirability bias of the patient. Moreover, the results are subject to recall bias particularly when the specified duration for the recall is long.

Prescription refill records: It may be used to evaluate medication adherence by calculating the medication possession ratio for the period from index fill to subsequently the next refill

Pill count method: The medication bottle or strips dispensed during the previous visit are brought by the patient. The number of pills taken is calculated by subtracting the count of the number of pills remaining from the total number of pills dispensed. The drug adherence rate is then calculated by dividing the number of pills taken by number of days elapsed since the last dispense.

Both the above methods for assessing medication adherence have several limitations. They only determine the possession of medication and not actual consumption by the patient. Moreover, their accuracy is also subject to the patient affirming having run out of the drug stocks and not having made any retail purchase of the medications during the intervening period, which is neither procedurally difficult nor uncommon in the context of Indian healthcare settings.

A further limitation of the study is the lack of use of multiple methods for the assessment of medication adherence in the HIV patients which is the recommended methodology.[25]

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Conflicts of interest

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